In the field of medical technology, there are a large number of known pieces of apparatus by which, via tubing, fluids can be fed to a patient or fluids can be fed out of the patient. Access is generally gained to the patient in this case by means of a catheter for introduction into organs of the body or by means of a canula or needle for puncturing vessels. It has to be ensured that there is proper access to the patient during examination or treatment. It is therefore necessary for the access to the patient to be monitored.
An application which makes particularly severe demands on the safety of the access to the vessel is extra-corporeal blood treatment in which blood is fed out of the patient via arterial tubing which has an arterial puncturing canula, the blood is conveyed through a dialyser, and is fed back to the patient via venous tubing which has a venous puncturing canula. Even though the access to the patient is regularly monitored by the hospital staff, there is basically a danger in this case of the venous puncturing canula slipping out of the patient's blood vessel unnoticed. Whereas if the arterial canula slips out this involves air being drawn into the arterial tubing, which results in a visual and/or optical alarm being given due to the detection of air by the machine and in the treatment being interrupted, the slipping-out of the venous canula, and the free flow of blood into the surroundings of which there is then a danger, cannot readily be detected. However, if the slipping-out of the venous canula is not detected immediately, the patient may exsanguinate.
There are a large number of different arrangements in the prior art for solving this problem. Some of these arrangements have recourse to safety arrangements which are present as standard in the blood treatment machines and cause an immediate interruption of the extra-corporeal circulation of blood if there is a vascular access which is not in a proper state. The safety arrangements which are present as standard in treatment machines are generally based on monitoring the pressure in the extra-corporeal blood circuit. However, it has been found in practice that the slipping-out particularly of the venous puncturing canula cannot be detected with sufficient reliability simply by monitoring the pressure in the extra-corporeal blood circuit. It is true that some known safety arrangements do have adequate sensitivity but they also react very sensitively to changes in the patient's position, which often results in false alarms. It is also a disadvantage that existing pieces of blood treatment apparatus cannot readily be retrofitted with the known monitoring arrangements and instead the retrofitting calls for a complicated and cost-intensive incursion to be made into the treatment apparatus.
International Patent Publication No. WO 2007/104350 A1 describes an easily operated arrangement which can be produced inexpensively and retrofitted at any time and which allows an access to a patient to be monitored safely and reliably. The monitoring of the access to the patient is based on the forming of a loop in the fluid-carrying tubing. It is assumed that slipping-out of the puncturing canula or the catheter is attributable to tractive forces being applied to the tubing. When the tubing is stressed in traction, the loop is necessarily pulled closed. This results in an increased pressure drop in the tubing and this is easy to detect.
Special fixing means are used to fix the tubing in the form of a loop. International Patent Publication No. WO 2007/104350 A1 describes two alternative embodiments which differ in that in one embodiment the fixing means are fixing pieces which are included loose with the tubing whereas in the other embodiment the fixing pieces are an integral part of the catheter for accessing the patient. The characteristic feature of the fixing pieces which are included loose is two eyes which are each used to receive a section of the tubing, the tubing being fixed in the form of a loop.
With the known fixing pieces, a section of the tubing can be fixed in the form of a loop which contracts under a tractive stress. It is a disadvantage however that the tractive force required for this is relatively high.